Hypericum androsaemum - yellowing leaves

Hi could anybody please tell me why my Hypericum androsaemum's leaves are turning yellow? I have had it for 5 -6 years and have never noticed it happening before. It is in a semi shaded position. Do I need to use a fertiliser or something more radical. I prefer not to use toxic chemicals as I have some nice wildlife visiting the garden. Please help if you can. Thank you

I think alot of the plants are suffering from too much rain fall and lack of sun,(the same as us) and if you wish to use a fertilizer ,I make my own from either nettles or comfrey,( cut leaves in a bucket of water for 2 wks ,tip water into another container and dilute very little in a gallon of water and feed plants every 2 wks in summer).I have many plants with yellow leaves and I have fed those so I think it must be too much rain.